Hippocampal injury in patients with status epilepticus: Quantitative analysis of hippocampal volume and structural co-variance network

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This study aimed to evaluate the differences in hippocampal structural volumes and intra-hippocampal networks between patients with status epilepticus (SE) and healthy controls. We enrolled 45 patients with SE and 35 age- and sex-matched healthy controls. We excluded patients with active structural lesions, which could be a direct cause of SE, but included patients with co-existing lesions. Co-existing lesions were defined as any lesions possibly related to the occurrence of SE, including encephalomalacia, cavernous malformation, dural arteriovenous fistula, and normal pressure hydrocephalus, etc. We divided 45 patients into those with co-existing lesions (n=21) and those without co-existing lesions (n=24). We conducted a volumetric analysis using FreeSurfer (version 7), and the intra-hippocampal structural co-variance network was analyzed with a graph theoretical analysis based on the structural volumes of the hippocampal subfields. The structural volumes and intra-hippocampal structural co-variance networks were not different between patients with and without co-existing lesions. However, both structural volumes and intra-hippocampal structural co-variance networks were significantly different in patients with SE compared to healthy controls, and the ratio of the volume difference: [(volume of controls-volume of patients)/volume of controls] was highest in the left hippocampus (0.195), left amygdala (0.143), left thalamus (0.126), and right cortex (0.084). In addition, the global connectivity measurements including radius, diameter, eccentricity, and assortativity were significantly increased, and the small-worldness index was significantly decreased in patients with SE. Notably, structural volumes were negatively related to age but not to the duration of SE. Our study revealed significant alterations in structural volumes and intra-hippocampal structural co-variance networks in patients with SE compared to healthy controls, even though hippocampal atrophy was not evident on visual analysis; this is likely due to the direct effect of SE itself.